DESCRIPTION (Investigator's Abstract): The long term goal of this research is to understand the neurophysiological mechanisms underlying disorders human postural control in order to provide a scientific basis for the evaluation and rehabilitation of balance disorders in the elderly. This project will focus on the role of central mechanisms, such as predictive and instructional set, and peripheral mechanisms, such as somatosensory information, on motor learning and adaptation of postural movements for control of stance and step initiation. Specifically, this project addresses the scientific basis of two common strategies for balance rehabilitation: teaching stepping for balance recovery and use of a cane as a postural sensory aid. This project will determine to what extent triggered, automatic postural movements can be learned, are influenced by expectation, and can be affected by use of touch contact. we characterized postural deficits associated with well-defined central nasal ganglia or cerebellar) and Peripheral (somatosensory) degeneration as a model to understand postural dyscontrol in the elderly. A newly-developed, unique posture platform will allow us to displace subjects in any horizontal direction within or beyond the boundary for stepping for postural recovery. Bilateral surface reactive forces, joint kinematics, calculated joint moments, and surface EMGs will be used to quantify three- dimensional, dynamic strategies for leg, trunk, arm, and head coordination during externally-imposed and self-initiated displacements of standing subjects. The specific aims are: I. Normal Postural Coordination: To investigate the role of central and peripheral neurophysiological mechanisms on specifying the direction of postural responses and coordinating stepping for postural recovery. Three experiments with healthy subjects will investigate the principles for 1) specifying postural direction, 2) coordinating stepping for postural recovery, and 3) modifying automatic stabilizing responses by intent to step. II. Central Motor Disorders: To characterize the effects of basal ganglia and cerebellar disorders on control and modification of step initiation for postural recovery. Studies will determine how patients with Parkinson's disease on and off levodopa and patients with anterior lobe cerebellar degeneration coordinate and learn stepping for postural correction compared with healthy elderly subjects. III. Peripheral Sensory Mechanisms and Disorders: To determine how somatosensory formation uses predictive and reactive mechanisms to modify automatic postural responses. We will test the hypothesis that use a cane will help patients with somatosensory loss due to diabetic peripheral neuron scale the magnitude and shorten the latency of postural responses to surface displacements. The role of cutaneous touch contact as an orientation reference for improving dynamic postural stability under various conditions will be examined in healthy subjects. A better understanding of the ability to modify automatic balance recovery strategies will provide the scientific ration for balance retaining programs for elderly and neurological patients with disequilibrium..